Summary Middle-aged adults often report problems understanding speech in adverse listening conditions, even though they typically demonstrate essentially normal results on routine audiological tests. The extent of these self- reported problems can be as great or greater than problems expressed by older adults with considerably more hearing loss. The disconnect between measured and self-perceived hearing problems in middle-aged adults could be due, at least in part, to listening being more effortful for them. Since their problems are not apparent using currently-available assessment measures, clinical audiology has little to offer these individuals in terms of identifying or addressing their hearing problems. The long-term goal of this research is to develop evaluation and treatment methods that focus on functional hearing early in the aging process. Treating hearing problems in midlife could help to reduce the negative outcomes associated with age-related hearing loss (such as cognitive decline and risk of incident dementia). The focus of the project described in this application is on quantifying cognitive load (i.e., effort) required for middle-aged adults to understand speech in the presence of different types of masking sounds. Cognitive load will be quantified using ecologically-valid measures: dual- task costs associated with listening-while-walking; memory for previously heard speech; and subjective ratings of listening effort. This project also will identify the impact of Personal Sound Amplifier (PSAPs) on functional hearing in middle-aged adults with mild hearing loss. These devices, which are sold over-the-counter, are more affordable than traditional hearing aids and so might be more acceptable to these individuals than are conventional hearing instruments. Experiments in the proposed project will determine the effectiveness of selected higher-end PSAPs (when used both binaurally and monaurally) for decreasing listening effort, and for improving speech understanding and spatial hearing ability, in middle-aged adults with mild hearing loss. Testing will be conducted before and after controlled field trials of monaural and binaural PSAP use in order to identify acclimatization effects. Outcomes of this project have the potential to alter when and how we evaluate and treat age-related hearing loss.